The invention relates to a process and a device for the separation of materials which are tenaciously elastic at normal temperatuze, such as plastics and rubber, from other materials defiberizing under high mechanical stress, such as paper, cardboard, carton or other products containing cellulose fibers.
More specifically, in waste disposal and recovery of substances contained in the waste materials, the separation of plastics and paper represents a considerable problem. Such mixed waste containing both plastics and paper or other cellulose products arises in huge amounts. Thus, for example, the presorted plastic packages from the collections conducted by Duales System (Germany), and particularly the so-called mixed fraction, have a significant percentage of paper, including paper labels, erroneous classifications in sorting, and paper-plastic composite materials.
To date, the separation of plastics, rubber and other tenaciously elastic materials from materials containing cellulose fibers, such as paper, cardboard and carton has been effected using the wet separation process which works by extensive defiberization of the fiber matrix and subsequent separation resulting in at least two streams of material, namely, the cellulose-containing sludge having a high water content, and the water-insoluble plastics. This process requires a considerable input in energy and machinery. In the above case, the paper defiberization is performed in a wet-grinding mill, for example, and in the shredding procedure, water is added exceeding the weight of plastics and paper by a multiple. Here, in particular, a huge amount of energy is required to set the masses of water in motion. So-called friction separators are used to separate the arising sludge of fillers, contaminants or other substances from the plastics. In each case, the mass flow rich in fibers must be dehydrated using vibrating or bottom screens, for example. In addition, the water content is usually reduced by pressing such as chamber filter pressing; however, a water content as high as more than 50% still remains in the product. If the mass high in paper fibers cannot be utilized, which is the normal case with waste materials, the high water content either causes high costs for dumping or considerable expenditure for drying in case of thermal utilization of the waste materials. Similarly, the plastics must be dehydrated, particularly if they are high in foils as is the case, e.g., with the combination of the abundant polyethylene foils with paper, which is predominantly effected by means of mechanical dryers. To this end, modified centrifuges or whizzers are used. In some cases, thermal (after) drying may be required so that in total, the expenditure for separation causes considerable cost and is ecologically unfavorable due to the high input in energy.
Numerous investigations have been conducted in this field. As examples, there may be mentioned: Louis Jetten, Stoffliches Kunststoffrecycling und die Rolle des Wassers in Aufbereitungstechnik beim Verwerten von Kunststoffen, VDI-Verlag, Dxc3xcsseldorf, 1993; and technological study: Stoffliches Kunststoffrecycling, Part 2, edited by EWvK, Entwicklungsgesellschaft fxc3xcr die Wiederverwertung von Kunststoffen, Wiesbaden, 1992.
Furthermore, processes for dry separation of paper and plastics operated utilizing electrostatic charging are already known. Here, separation using a gravity separator may be mentioned, which is described in DE 3,227,874 and DE 4,225,977, for example. This process involves considerable drawbacks. The charging material is required to meet quite specific preconditions regarding the geometrical dimensions. Also, the demands with respect to the drying level are very high. The operative input is considerable. Moreover, this process does not permit separation of non-positive and positive composite materials.
Therefore, it is the object of the invention to provide a process for the separation of tenaciously elastic materials such as plastics and rubber from materials defiberizing under high mechanical stress, such as paper, cardboard and carton, which is advantageous in ecological terms and simple in processing technology. For example, LDPE, HDPE, PP, polystyrene, PVC, PET, and ABS may be mentioned as plastics.
Surprisingly, it was found possible to separate tenaciously elastic materials such as plastics and rubber from fiber-containing materials such as paper in an essentially dry and technically simple fashion by impinging the mixture of plastics and fiber-containing material using high acceleration and impact forces, the fiber-containing material being ripped and/or defiberized by the action of said forces, discharging through the appropriate openings of a screen basket, while the non-defiberizing plastics remain in the interior of the casing and are removed in axial direction. The application of acceleration and impact forces or the use of a centrifuge in the dry separation of paper and plastics must be rated surprising because centrifuges have invariably been used for separating solid-liquid phases or liquid-liquid phases.